Why do int keys of a python dict turn into strings when using json.dumps?

The simple reason is that JSON does not allow integer keys.

object
    {}
    { members } 
members
    pair
    pair , members
pair
    string : value  # Keys *must* be strings.

As to how to get around this limitation – you will first need to ensure that the receiving implementation can handle the technically-invalid JSON. Then you can either replace all of the quote marks or use a custom serializer.